The field of the invention is machines for making food products, such as pizzas.
Pizza shells or crust are made from a dough, typically with wheat flour. For large scale production, the dough is prepared in large batches, and individual doughballs are formed. To make a pizza, the dough must first be molded or flattened to the proper shape and thickness. For hand-made pizza, the dough is flattened by pressing it and stretching it, and via the ever popular pizza hand xe2x80x9ctossxe2x80x9d. Small presses may also be used. For large scale production, a common method for forming pizzas is to press the dough in a pressing machine having one or more pizza dies.
For most pizzas, the pressed pizza dough should preferably produce a finished food product that is close in taste and texture to a hand-made pizza dough. For example, it is preferable that the pressed dough retain its shape after formation. In addition, the pizza should also preferably bake as a hand-made pizza. For instance, it is often preferable that the dough rise during baking, particularly in the crust region of the dough, for so called xe2x80x9crising crustxe2x80x9d pizza.
Various attempts have been made to produce pizzas having these characteristics. One method uses multiple dies within a press to flatten the pizza dough. The press exerts a large pressing or flattening force on the dough ball. One common design has an inner die plate within a larger outer die ring. Typically, the inner die further includes a groove around its outer edge to form a ridge, or crust, in the pizza dough. The outer die ring very closely surrounds the inner die.
However, this design has a number of disadvantages. To prevent extrusion of pizza dough through the small gap between the inner die plate and the outer die ring, these components must be machined to extremely close tolerances. This increases the cost of production.
Usually, during pressing, the dough is also heated by heaters on or around the pizza die. However, the heating of the pizza die causes inner die plate and outer die ring to expand at different rates. This expansion of the components requires additional clearance between the inner die plate and outer die ring, to prevent them from seizing or binding. Unfortunately, the increased clearance also tends to permit dough to extrude through the annular gap between them.
Due to the close fit between the inner die plate and the outer die ring, the non-stick coating typically used on these surfaces wears off relatively quickly. This causes the pressed pizza dough to stick to the die, thereby stopping the production line. In practice, removal of the stuck dough from the die generally requires use of makeshift tools, that tend to scratch even more of the non-stick coating off of the die. Once the dough begins to stick, some manufacturers will use higher temperatures and/or longer dwell times to achieve better release characteristics, thereby producing a xe2x80x9chot pressed pizzaxe2x80x9d. However the additional heat produces skin and core temperatures which kill most or all of the yeast in the dough. This prevents the dough from rising when baked.
If the fit between the inner die plate and the outer die ring is too loose, the pizza dough will extrude through the gap during the pressing operation. This causes the pizza dough to stick to the pizza die, also stopping the production line.
On the other hand, if the fit between the inner die plate and outer die ring is too close, excessive heating in the outer die ring results, even though the heating elements are in contact only with the inner die plate. Often, it is preferable for the pizza dough to rise during baking, e.g., for xe2x80x9crising crustxe2x80x9d pizza. If the outer ring gets too hot, the yeast in the dough near the outer ring will be killed, thereby, preventing the crust from rising as desired. The close fit of the inner die plate and outer die ring can prevent the desired thermal isolation of the outer die ring.
Another problem encountered in this design relates to the venting of trapped air within the die during pizza formation. Typically, there are grooves located along the bottom face of the outer die ring. The grooves are designed to exhaust the trapped air. Unfortunately, these grooves are frequently blocked by the pizza dough before the trapped air can exit the pizza die. This occurs because the pizza dough has a more direct route through the radial grooves in the outer die ring. It takes a longer amount of time for the pizza dough to travel to the upper groove area in the outer circumference of the inner die plate where the lip of the pizza is formed.
Producers using the traditional inner die plate and outer die ring must balance several factors. For instance, proper pizza formation requires a particular pressure depending on the type of pizza dough. If the pressure is too high, pizza dough extrudes out the gap formed between the inner die plate and the outer die ring. This remains true even if a seal is present between the inner die plate and an outer die ring. The problem is further compounded since trapped air reduces the flow rate of the dough within the die. Consequently, higher pressures are required to overcome this resistance.
For these reasons, the food industry needs better machines and methods for making pizzas, and other food products.
In a first aspect of the invention, a pizza die includes a die mount plate, an outer die ring, and an inner die plate within the outer die ring. The outer die ring and the inner die plate are attached to the die mount plate. The inner die plate includes an angular step around its circumference. A flexible seal is seated on the angular step and is held in place via plate ring. The plate ring and outer die ring are spring-biased away from the die mount plate.
In a second aspect of the invention, a pizza die includes a die mount plate, an outer die ring, and an inner die plate. The outer die ring includes a plurality of axial ridges located on a portion of the inner circumferential surface of the outer die ring. The inner die plate includes a step around the outer circumference of the inner die plate. A flexible seal is seated on the step. The flexible seal includes axial grooves along its outer circumference, wherein the axial grooves correspond to the axial ridges located on the outer die ring. A plate ring is sandwiched between the die mount plate and the flexible seal and provides an axial compressive force on the flexible seal.
In a third embodiment of the invention, the pizza die of the second aspect has the outer die ring and the plate ring spring-biased away from the die mount plate.
It is an object of the invention to provide improved apparatus and methods for making pizzas and similar pressed food products.